1. Field of the Invention
The present invention relates to an ultrasonic diagnostic apparatus and program for extracting and displaying a minute structure in a living body organ from an echo signal of tissue.
2. Description of the Related Art
In ultrasonic diagnosis, heart beats and fetal movements can be displayed in real time through a simple operation of placing an ultrasonic probe over the surface of a body. Since ultrasonic diagnosis has a high level of safety, ultrasonic diagnostic tests can be performed repeatedly. Further, an ultrasonic diagnostic apparatus is smaller than other diagnostic apparatuses employing X-rays, CT, and MRI, for example. Thus, ultrasonic diagnosis is a simple and easy diagnostic scheme, allowing the ultrasonic diagnostic apparatus to be easily moved to the bedside for diagnosis, for example.
Ultrasonic diagnostic apparatuses vary greatly depending on the kind of functions equipped therein. Among compact types, ultrasonic diagnostic apparatuses which can be carried with one hand have been developed. Unlike the use of X-rays, for example, ultrasonic diagnosis is free from the influence of exposure to radiation, and can be used in obstetrics or home medical care, for example.
One of ultrasonic diagnoses offering various advantages as described above is early diagnosis for breast cancer. It is known that microcalcifications occur in breast tissue with a high frequency as a sign of breast cancer. One or more microcalcification lesions are topically scattered. Since calcium is higher in hardness than body tissue, calcium reflects ultrasound well. Microcalcification lesions should therefore have high brightness on an image. In actuality, however, when an image is observed by the eye, it is said that microcalcification lesions even with the size of approximately several hundred microns are difficult to be detected.
On an ultrasonic image, interference fringes called a speckle pattern, which is caused by random interference of ultrasound, may occur. A speckle pattern is used for diagnosis of cirrhosis.
A speckle pattern closely resembles microstructures which are often overlooked in a diagnosis for breast cancer, and can be confusing image information for diagnosis in some cases. Thus, in a diagnosis for breast cancer, there is a need for removal of a speckle pattern.
In view of the above-described circumstances, techniques such as spatial compounding, a constant false alarm rate (CFAR) process, and similarity filtering. The spatial compounding is a process of superimposing transmission and reception signals from different directions and smoothing speckles. The CFAR process is a process of subtracting a neighboring average of brightness from the target pixel, and uses the subtracted result to extract high-brightness portions. The similarity filtering is a process of removing speckles using its statistical properties. As well as the above-described techniques for removal of speckle patterns, in fields other than the ultrasonic diagnosis, various attempts to automatically recognize microcalcifications have been reported mainly as applications of X-ray diagnosis images.
The mammary gland, which is a target of a diagnosis, has a complex structure especially in the lactiferous duct, for example, and is not a homogenous organ in nature. Thus, according to the conventional filtering process, upon detection of microcalcifications, the mammary gland structure is also extracted as a structure, and the two cannot be distinguished sufficiently.
Since structures such as the lactiferous duct are clearly larger than microcalcifications, the two can sometimes be distinguished by the eye even if the lactiferous duct remains after the filtering process. However, the inventors have often experienced difficulties in making such a distinction in research. In particular, when only a part of the mammary gland structure remains, the remaining mammary gland structure may look similar to microcalcifications, since the mammary gland structure is shown as dots on an image after the filtering process.
Furthermore, a speckle pattern on an image may vary randomly. In such a case, even after performing a predetermined speckle reduction process, speckles remain, which makes it difficult to distinguish between the remaining speckles and calcified parts.
In view of such circumstances, Japanese Patent KOKAI Publication No. 2007-313114 discloses the following technique. That is, Japanese Patent KOKAI Publication No. 2007-313114 discloses an ultrasonic diagnostic apparatus for image processing of extracting a microstructure using a first ultrasonic image and a second ultrasonic image determined based on the position of the first ultrasonic image, comprising an image processing means for generating a microstructure-extracted image by performing a microstructure extraction process of calculating a difference from a maximum pixel value of a reference region in the second ultrasonic image including a spatially corresponding pixel, with respect to each pixel in the first ultrasonic image, and display means for displaying the microstructure-extracted image in a predetermined form.
According to the ultrasonic diagnostic apparatus disclosed in Japanese Patent KOKAI Publication No. 2007-313114, by using spatial three-dimensional information instead of a slice of a tomogram in signal processing, continuous structures such as the mammary gland and microstructures such as microcalcified parts are accurately distinguished, and the microstructures can be extracted.
An ultrasonic probe used in the technique disclosed in Japanese Patent KOKAI Publication No. 2007-313114 is capable of ultrasonically scanning a three-dimensional region of a test body. Accordingly, ultrasonic probes used in the technique disclosed in Japanese Patent KOKAI Publication No. 2007-313114 include an ultrasonic probe (referred to as a mechanical 4D ultrasonic probe) with a configuration in which a vibrator mechanically vibrates in an orthogonal direction of its arranging direction and a three-dimensional region is ultrasonically scanned, and an ultrasonic probe (referred to as a real-time 3D ultrasonic probe) with a configuration in which a three-dimensional region is ultrasonically scanned by electric control using two-dimensional vibration elements arranged two-dimensionally.
In the mechanical 4D ultrasonic probe, the test body is three-dimensionally scanned by the vibrator circuit. The tester can therefore automatically acquire a plurality of two-dimensional tomograms only by making the main body of the ultrasonic probe contact the test body. Further, an accurate distance between the cross-sections can also be detected from the controlled vibration rate. In the real-time 3D ultrasonic probe, on the other hand, a three-dimensional region can be ultrasonically scanned in principle in a time same as that required for acquiring the conventional two-dimensional tomograms.
Because of the size and weight, however, the mechanical 4D ultrasonic probe has problems of difficulty in scanning for capturing a minute structure and insufficiency in real-time properties. Further, the real-time 3D ultrasonic probe conceivably requires further time for development.
Accordingly, under the present circumstances, a technique by which a diagnosis result of a clinically permissible level (at which a microstructure can be extracted), using a conventional 1D ultrasonic probe (including a 1.5D ultrasonic probe) as an ultrasonic probe, is strongly desired. In other words, a technique by which a desired microstructure-extracted image can be obtained in real time using a 1D ultrasonic probe, which is the most common ultrasonic probe, is desired.